1. Field of the Invention
The present invention relates to a stacked semiconductor device having an improved structure for heat dissipation.
This application is based on patent application No. Hei 10-170348 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
Ordinary stacked semiconductor devices comprise semiconductor chips 11a and 11b, module substrates 12a and 12b, and a mother board 14 as shown in FIG. 9. The semiconductor chip 11a is flip-chip mounted to the module substrate 12a, whereby a module is obtained. Similarly, the semiconductor chip 11b is flip-chip mounted to the module substrate 12b, whereby another module is obtained. Module-stacked body is obtained by stacking these modules. The module-stacked body is stacked on the mother board 14 via connectors 13 as shown in FIG. 9.
The connectors 13 are positioned in the spaces between the module substrates 12a and 12b, and the module substrate 12a and the mother board 14. Therefore, the semiconductor chip 11a does not contact the module substrate 12b, and the semiconductor chip 11b also does not contact the mother board 14. When the semiconductor chip 11a contacts the module substrate 12b, and the semiconductor chip 11b contacts the mother board 14, the mother board 14 expands due to heat generated by the semiconductor chips 11a and 11b, or by rising ambient temperature. The semiconductor chips 11a and 11b are then subjected to excessive pressure, whereby the semiconductor chips 11a and 11b may be damaged. In order to prevent such damage, only one surface of the semiconductor chip 11a contacts the module substrate 12a, and only one surface of the semiconductor chip 11b contacts the module substrate 12b. That is, there is a space between the other surface of the semiconductor chip 11a and the module substrate 12b. There is also a space between the other surface of the semiconductor chip 11b band the mother board 14.
It is believed that air flows into the spaces; therefore, most of heat generated by the semiconductor chips 11a and 11b can be dissipated. Therefore, ordinary semiconductor devices do not comprise special structures for heat dissipation.
Another ordinary semiconductor device comprises the semiconductor chips 11a and 11b mounted on the module substrates 12a and 12b as shown in FIG. 10. That is, the semiconductor chip 11b is mounted on the module substrate 12b so that the semiconductor chip 11b does not face toward the mother board 14. In order to prevent the damage to the semiconductor chips 11a and 11b by heat, only one surface of the semiconductor chip contacts the module substrate. That is, there is a space between the semiconductor chip 11b and the module substrate 12a.
As described above, most of heat generated by the semiconductor chip is dissipated in the each module; therefore, heat dissipation efficiency of the semiconductor device is low. As a result, the temperature of the operating semiconductor chip becomes high and the semiconductor chip may malfunction. In some cases, the semiconductor chip may be damaged.
It is therefore an object of the present invention to provide a stacked semiconductor device which has an improved structure for heat dissipation and can operate stably semiconductor chips.